Hints on implementing iOS-compatible L2CAP peripheral

RE: Hints on implementing iOS-compatible L2CAP peripheral

tangobravo — Fri, 30 Sep 2022 14:53:58 GMT

Hi Simon,

Thanks for the reply.

[quote userid="75734" url="~/f/nordic-q-a/92444/hints-on-implementing-ios-compatible-l2cap-peripheral/388741"]This sounds interesting indeed, although as this sounds like it would be a stack of its own, and I think there will also be a lot of work required to get it certified in the end.[/quote]

I don't quite follow here - I thought L2CAP was just the link layer of BLE, so still the same BLE stack and it should be able to operate at the same time as the higher-level GATT stuff? We're using a Raytac module rather than the nRF directly.

I did try to capture a trace of the iPod to iPhone implementation, but it seems even though I didn't explicitly pair them they still seem to have some shared key somehow (perhaps via iCloud or something). Attached it anyway FWIW.

The code for both of the iOS apps is on GitHub:

https://github.com/tangobravo/ios-bluetooth-peripheral

https://github.com/tangobravo/ios-bluetooth-central

Thanks for the other advice, I'll have a deeper look into those docs and see if I can get anything running.

devzone.nordicsemi.com/.../iPod_2D00_to_2D00_iPhone12.pcapng

RE: Hints on implementing iOS-compatible L2CAP peripheral

Simonr — Fri, 30 Sep 2022 10:58:34 GMT

This sounds interesting indeed, although as this sounds like it would be a stack of its own, and I think there will also be a lot of work required to get it certified in the end.

In variant 4, the le_psm parameter is actually ignored in the variant 4, as it's only used when requesting the setup of an L2CAP channel, and ignored otherwise. When that's said, the SoftDevice won't check the le_psm, and it's up to the peer to accept it, which means you're free to hardcode this parameter from the nRF point of view.

As far as what documentation to look at, I think you're on the right track with the L2CAP API reference available on the Infocenter.

Best regards,

Simon

RE: Hints on implementing iOS-compatible L2CAP peripheral

tangobravo — Thu, 29 Sep 2022 14:05:50 GMT

To get a bit more specific, I've been looking at the message charts here:

https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s113.api.v7.3.0/group___b_l_e___l2_c_a_p___c_h___s_e_t_u_p___m_s_c.html

I assume to recreate the iOS flow (where the central initiates the connection) we'd be looking at variant 4.

It looks like in that case the central specifies the PSM to connect to. Can this PSM be hardcoded (and if so, what are the valid values). If it's dynamic (like in the iOS peripheral API) then how do I allocate and query the PSM for a channel?